Kenwood TK-701S Service Manual page 24

[K-701S
5. Modulator circuit
The transmitter PLL reference (or OFFSET) oscillator
Q12: 2SC2668(Y) is directly frequency modulated. An
EIA (RS-152-B) frequency modulation characteristic is
obtained by mic amplifier-limiter U24 and U25 (both
uPC4558C).
05
6. PLL unlock detection circuit
Unlock condition is detected in the common PLL by
Q7: 2SC2603(E) and in the transmit PLL by Q16:
2SC2603(E). When either PLL unlocks, an "UNL" voltage
at J1 pin 16 of approximately 8V deactivates the transmit-
ter driver stages to prevent "illegal" output.
ai
UNLOCK DET
QI6
a UI9
Ql Q2
UNLOCK DET
Q7
Q3 Jil
3RXO
tI
J23
U
UNLOCK SW
Q5
LI
I
!
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I
| UNL] 16
fl
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|
i
!
TX .RX UNIT
Fig. 4-13 Unlock Detection Circuit
7. QTD invert circuit
To select polarity (active Low or active High) to con-
trol QTD, Q17: 2SC2603{E) can be un-strapped to oper-
ate as an inverter.
8. TX frequency shift circuit
In the duplex mode, the first address bit (B4) is set to
logic high by Q8: 2SC2604(E) in order to change the data
(i.e. change address) in the PROM during transmission. In
. 6-channel operation, the duplex channel can be selected
only from CH1 through CH6 by shift diodes D10 to D15:
all 1$1555. (Channels slots in which diodes are installed
are duplex.)
9. Diode matrix
Diodes D16 through D22 (all 181555) form a matrix
circuit which converts the rotary channel switch status to
PROM address data during 6-channel operation.
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